THE HISTORY AND SHAPE OF THE TEST-PIECE. 337
"with shorter bars, and this proves that the specified decrease in elongation for an increase in length is not greater than should justly be allowed. In the bars made by "A" the rejections amount to 4 per cent, in Bessemer metal, and 3 0 per cent, in open-hearth; in those made by "B" they are 10 per cent, in the Bessemer and 20 per cent, in the open-hearth, while with "Q" they are 23 per cent. Taking into consideration that the records cover only the products of large and well-known works, and that all bars having a crystalline fracture and those breaking in the eye were discarded, it must be acknowledged that the standard specifications call for good material.
SEC. XVII.—Alterations in steel ~by rest after rolling.—In addition to the variations caused by differences in the working of the test-piece and in its shape, there is another factor in the length of time which elapses between rolling and testing. This subject was investigated at The Pennsylvania Steel Works by E. C. Felton, now president of the company, a condensation of whose work is given in Table XVI-IT. The changes are not strongly marked, but there seems to be a molecular rearrangement, for several hours after the bar is cold, whereby there is a lowering of the elastic limit, and an increase in the ultimate strength, the elongation, and the reduction of area.
SEC. XVIm.—Errors in determining the physical properties.— It is the rule in practical work that two sides of the test-piece are not machined, and hence it is impossible to make a perfectly accurate measurement. In order to find how great an' effect may be caused by such errors and by differences in machines and-the method of operating them, the experiment was tried of sending a bar from six different acid open-hearth heats to six different testing laboratories. The pieces were rolled flats, 2"x f", and each series was made up of one piece from each of the six bars.
All pieces were tested in the shape in which they left the rolls without machining, and although the edges were not perfectly smooth, they were so nearly true that only one operator referred to any difficulty in making a true measurement. Table XVI-V exhibits the results reported. The bars were tested by The Central Iron and Steel Works, Harrisburg, Pa.; The Baldwin Locomotive Works, Philadelphia,, Pa.; The Pottstown Iron Company, Potts-town, Pa.; The Carnegie Steel Company, Pittsburg, Pa.; The Car-